1. Field of the art
This invention relates to a coupler for photography, more particularly to a 2,5-diacylaminophenol type cyan coupler which is suitable for a light-sensitive silver halide color photographic material.
2. Prior art and its problems
Ordinarily, in light-sensitive silver halide color photogaphic materials, silver halide grains exposed to light are reduced with an aromatic primary amine type color developing agent, and dye images can be obtained through coupling of the oxidized product of the above-mentioned color developing agent which has been thereby formed with couplers for forming respective dyes of yellow, magenta and cyan.
The cyan couplers widely employed for formation of the aforesaid cyan dyes are phenol type and naphthol type couplers. In particular, the first point to be improved in phenol type cyan couplers to be utilized for final images is to have good spectral absorption characteristics of cyan dyes, more specifically to have weak absorption in the green region (particularly at 500 nm-550 nm) of the absorption with the maximum absorption wavelength being at longer wavelength region (640 nm-660 nm). Secondly, the cyan dye formed should have sufficient fastness to light, heat and humidity, and staining at the portion without color formation should be little under these storage conditions. Thirdly, it is also required to have good color forming property, namely sufficient color forming sensitivity and color forming density. And, fourthly, color loss should be small even when the bleaching bath or bleach-fixing bath comprising ferric EDTA salt as the main component may be fatigues after usage for a long term.
A large number of proposals have been heretofore been made to improve these points. Particularly, as the cyan couplers which are attracting attention for excellent characteristics with respect to the fourth point as mentioned above, there are 2,5-diacylaminophenol type cyan couplers. Illustrative of such cyan couplers are 2,5-diacylaminophenol type cyan couplers having a fluorine-substituted aliphatic carboxylic acid amido group at the 2-position of phenol and an acylamino group at the 5-position as disclosed in U.S. Pat. Nos. 2,772,162 and 2,895,826. These 2,5-diacylaminophenol type cyan couplers known as specific compounds are indeed excellent in heat resistance of cyan dyes formed and also excellent in spectral absorption characteristics, but they involve vital drawbacks that they are markedly inferior in color forming properties of the couplers per se and light resistance of the dyes formed. Accordingly, for improvement of these drawbacks, the so called two equivalent couplers have been proposed, in which fluorine atoms is introduced at the 4-position where the coupling reaction occurs between the color developing agent and the oxidized product, as disclosed in U.S. Pat. No. 3,758,308. These couplers, while they exhibit excellent color forming properties, have undesirable properties that yellow staining will be formed by light.
Also, U.S. Pat. Nos. 3,758,308 and 3,880,661 disclose 2,5-diacylaminophenol type cyan couplers having a pentafluorobenzamido group at the 2-position of phenol ring. On the other hand, 2,5-diacylaminophenol type cyan couplers having o-sulfonamidobenzamide group at the 2-position of phenol ring are disclosed in Japanese Provisional Patent Publication No. 80045/1981. These diacylaminophenol type cyan couplers are satisfactory with respect to spectral absorption characteristics, but not necessarily sufficient with respect to fastness of dyes.
Also, 2,5-diacylaminophenol type cyan couplers having a sulfonamido group at the 5-position of phenol ring have also been developed, as disclosed in Japanese Provisional Patent Publication Nos. 109630/1978, 163537/1980, 22235/1981, 99341/1981, 116030/1981, 55945/1981 and 80054/1981. Further, Japanese Provisional Patent Publication No. 161542/1981 discloses 2,5-diacylaminophenol type cyan couplers having a benzamido group substituted with at least one fluorine atom at the 2-position of phenol ring. Whereas, the dyes formed from these couplers are excellent in fastness but insufficient in spectral absorption characteristics.
The present inventors have made extensive studies in order to remove the above-mentioned drawbacks possessed by the 2,5-diacylaminophenol type cyan couplers of the prior art, and consequently found that a certain class of 2,5-diacylaminophenol type couplers having an arylacylamino group at the 2-position are excellent inspectral absorption characteristics and markedly improved in image storability. These couplers are already described in U.S. patent application Ser. No. 520,556. These couplers have overcome the various drawbacks as mentioned above, but they are insufficient in solubility in organic solvents when dissolved or dispersed with the use of an organic solvent such as ethyl acetate and therefore a large amount of such a solvent is required to be used. Another inconvenience was also found to be involved that cyan couplers became precipitated, if the gelatin emulsion after dispersing was not maintained at a high temperature. Accordingly, production of photographic materials on an industrial scale with the use of the cyan couplers involving such inconveniences will impair markedly productivity thereof. Now, as the method for improvement of solubility, it may be considered to introduce a straight and long chain alkyl group into the acylamino group at the 5-position. However, as the result of investigation by the present inventors about the solubility of 2,5-diacylaminophenol type cyan coupler having introduced a straight and long chain alkyl group into the acylamino group at the 5-position, it was found to be still insufficient in solubility, and said coupler was also found to be difficulty purified. Solubility of the coupler was found to be further markedly improved by introduction of a long chain and branched alkyl group in place of the straight alkyl. In this case, however, since the carboxylic acid ester usually employed for introduction of such a long chain and branched alkyl has a high boiling point, purification of such a carboxylic acid ester becomes difficult. Consequently, there was the drawback that it was difficult to obtain a coupler of the final product at high purity, when such a carboxylic acid ester is used as the intermediate.